(1) Field of the Invention
The present invention relates to a marine reversing gear assembly.
(2) Description of the Related Art
Conventionally, a marine reversing gear assembly provided with a friction disk hydraulic clutch is known for use in small crafts, such as motorboats, fishing boats, and the like. Such a marine reversing gear assembly is disclosed in, for example, Japanese Patent Publication No. 1994-80098.
The marine reversing gear assembly is configured in such a manner that hydraulic oil pressure is applied to the friction disks of a forward clutch or a reverse clutch to press the friction disks against each other, and the rotation of an output shaft is transmitted to an input shaft, thereby forwarding and reversing crafts.
There are two means for exchanging the hydraulic oil pressure of the hydraulic clutch according to the forwarding or reversing motions. In one means, a directional control valve for hydraulic oil disposed in a hydraulic line is directly operated in a manual manner. In another means, the directional control valve is remotely controlled by operating an electromagnetic valve with an electric signal. The former means is disclosed in, for example, Japanese Patent Publication No. 1994-80098, and the latter means is disclosed in, for example, Japanese Patent Publication No. 1999-182582.
Among the above-mentioned directional control valves, the electromagnetic directional control valve is advantageous in that since remote control can be easily performed, crafts can be comfortably controlled as compared with crafts provided with the manually-operated directional control valve. However, the electromagnetic directional control valve has drawbacks in that it is susceptible to salt damage by sea water, and the function of the directional control valve tends to be spoiled by electrical shorts in the electrical circuit of the electromagnetic valve or by the malfunction of relay switches. When such failure arises, the spool of the electromagnetic valve needs to be directly operated by human power, which makes it quite difficult and troublesome to manage crafts. On the other hand, the manually-operated directional control valve is advantageous in such problems do not occur, and failures are rare.
Therefore, in view of the advantages of the forward/reverse directional control valve, requests are sometimes made to change the specifications of an already-installed directional control valve from a manual directional control valve to an electromagnetic directional control valve, or vice versa.
However, the manual directional control valve and the electromagnetic directional control valve have different spool structures. Conventionally, in order to avoid sudden engagement of the forward clutch or the reverse clutch when the forward/reverse directional control valve is changed, a kind of pressure control valve referred to as a loose-fitting valve is disposed in the hydraulic oil supply circuit. The manual directional control valve is integrally provided with a restrictor for the loose-fitting valve in its valve body, while the electromagnetic directional control valve is not provided with a restrictor. Therefore, changing the specifications of the already-installed directional control valve from a manual directional control valve to an electromagnetic directional control valve, or vice versa, requires replacing the marine reversing gear assembly itself or at least the entire oil passage block to which the directional control valve is installed. This results not only in wasting the marine reversing gear assembly itself or the parts installed therein but also requires much work for the replacement.
Small crafts, such as fishing boats, fishing leisure boats, and the like, are frequently required to travel at quite low-speeds for some uses. The following cases can be cited: stopping at fishing grounds; crafts stopping at a fixed point against a current without anchoring; traveling at a slow speed in accordance with the net hauling speed so as not to apply an excessive load to the net and to avoid tangling the net around the propeller during net hauling, etc.
As a device for achieving such travel, a marine reversing gear assembly with a trolling device provided with a friction disc hydraulic clutch is conventionally known. Such a marine reversing gear assembly with a trolling device is disclosed in, for example, Japanese Patent Publication No. 1994-80098.
The trolling device is configured in such a manner as to enable trolling by the slippage of the friction discs caused by lowering the hydraulic oil pressure applied to the friction discs of the forward clutch or reverse clutch, which can be suitably changed, and by lowering the ship speed by reducing the rotation of the output shaft to be less than that of the input shaft.
Conventionally, the hydraulic oil pressure is adjusted in a mechanical manner or in an electrical manner. More specifically, the hydraulic oil pressure is mechanically adjusted by a governor provided on a rotary shaft that is interlocked with the propeller shaft so as to rotate a propeller shaft at the number of revolutions corresponding to the ship speed during trolling. Alternatively, it is electrically adjusted by electrically detecting the number of revolutions of the propeller shaft, and electrically adjusting the hydraulic oil pressure of the hydraulic clutch to achieve the number of revolutions corresponding to the ship speed during trolling. The former case is disclosed in, for example, Japanese Patent Publication No. 1996-200405, and the latter case is disclosed in, for example, Japanese Patent Publication No. 2001-63692.
However, since the prior-art mechanical and electrical adjustment elements of the hydraulic oil pressure for trolling are different in the structure of the hydraulic oil circuit, the structure of the adjustment elements must be matched with either one of the hydraulic oil circuits at the manufacturing stage. Therefore, if the hydraulic oil adjustment element is changed from a mechanical element to an electrical element, or vice versa, after the installation thereof, the gear case itself for the trolling device must be replaced, resulting in wasting the hydraulic oil pressure adjusting element installed beforehand requiring much work for the replacement.
In some cases, trolling travel is not required depending on the intended use of the ship or craft. In that case, the mechanical or electrical hydraulic oil adjusting device installed beforehand is completely useless.